protect all functions from behaviour by default

[msz]

No description provided.

[msz]

#54 added protect/1 for behaviour-implementation modules but not closing this just yet as it would be good to also add a protect/2 version for when the behaviour and implementation modules are different modules. cc @saneery if you'd like to tackle this too

[saneery]

Sure! you may assign the issue to me

[saneery]

@msz should we return exceptions then some function inside the implementation module doesn't have specs? Or decorate only those with specs?
The second seems is more reasonable to me

[msz]

Often the implementation module will be much larger than a behaviour, and can actually implement several behaviours and still have its own functions. So I think if we are protecting with a specific behaviour, we should only look at callbacks from that behaviour.

[msz]

Closed in #55.